Emission cross sections and spectroscopy of Ho/sup 3+/ laser channels in KGd(WO/sub 4/)/sub 2/ single crystal

Abstract

The spectroscopic properties of Ho/sup 3+/ laser channels in KGd(WO/sub 4/)/sub 2/ crystals have been investigated using optical absorption, photoluminescence, and lifetime measurements. The radiative lifetimes of Ho/sup 3+/ have been calculated through a Judd-Ofelt (JO) formalism using 300-K optical absorption results. The JO parameters obtained were /spl Omega//sub 2/=15.35/spl times/10/sup -20/ cm/sup 2/, /spl Omega//sub 4/=3.79/spl times/10/sup -20/ cm/sup 2/, /spl Omega//sub 6/=1.69/spl times/10/sup -20/ cm/sup 2/. The 7-300-K lifetimes obtained in diluted (8/spl middot/10/sup 18/ cm/sup -3/) KGW:0.1% Ho samples are: /spl tau/(/sup 5/F/sub 3/)/spl ap/0.9 /spl mu/s, /spl tau/(/sup 5/S/sub 2/)=19-3.6 /spl mu/s, and /spl tau/(/sup 5/F/sub 5/)/spl ap/1.1 /spl mu/s. For Ho concentrations below 1.5/spl times/10/sup 20/ cm/sup -3/, multiphonon emission is the main source of non radiative losses, and the temperature independent multiphonon probability in KGW is found to follow the energy gap law /spl tau//sub ph//sup -1/(0)=/spl beta/exp(-/spl alpha//spl Delta/E), where /spl beta/=1.4/spl times/10/sup -7/ s/sup -1/, and /spl alpha/=1.4/spl times/10/sup 3/ cm. Above this holmium concentration, energy transfer between Ho impurities also contributes to the losses. The spectral distributions of the Ho/sup 3+/ emission cross section /spl sigma//sub EM/ for several laser channels are calculated in /spl sigma/- and /spl pi/-polarized configurations. The peak a /spl sigma//sub EM/ values achieved for transitions to the /sup 5/I/sub 8/ level are /spl ap/2/spl times/10/sup -20/ cm/sup 2/ in the /spl sigma/-polarized configuration, and three main lasing peaks at 2.02, 2.05, and 2.07 /spl mu/m are envisaged inside the /sup 5/I/sub 7//spl rarr//sup 5/I/sub 8/ channel.